Diesel is a middle distillate and a predominantly mineral fuel. Diesel fuel mainly consists of various hydrocarbons from crude oil, which are isolated by distillation from crude. It is a material fraction of crude oil, which is somewhere between light and heavy fuel oils. The fraction with a boiling point between 200°C and 360°C is referred to as gasoil. Diesel fuel is a refined gasoil. Blending brings gasoil to within the necessary parameters of the respective fuel standard. In addition to special additives, it is also blended with biofuels such as biodiesel. Currently, up to 7 vol.% biodiesel can be included in diesel fuel in accordance with DIN EN 14214. HVO (hydrogenated vegetable oils), GtL (gas-to-liquid) and BtL (biomass-to-liquid) fuels can also be admixed.

Consumers of diesel fuel are vehicles used for road transport, agriculture, shipping, and rail transport. Diesel is also used in construction and stationary engines.

The quality requirements for diesel fuel are defined in DIN EN 590. The requirement that diesel fuel sold at public filling stations must comply with DIN EN 590 is anchored in the 10thBImSchV (Federal Emissions Protection Act), which implements European Directive 98/70/EC (Directive on the quality of gasoline and diesel fuels). The climate zone a fuel is marketed in also plays a role, as cold weather can lead to paraffin precipitation in diesel fuels. For this reason, its composition varies in different countries. For example, in Germany a specific “winter diesel” is sold between November and February, but this is not usually mentioned at filling stations.

In large engines, especially marine diesel engines, heavier grades of diesel fuel are commonly used (see marine fuels), often with a higher sulfur content than diesel fuel for motor vehicles. The sulfur content of marine diesel (marine fuels) has not increased, however, but is increasingly being lowered due to the more stringent emission limits of current legislation (see ECA).